Refining of soybean oil



`Aug. 13, 1957 H. J. PAsslNo REFINING OF SOYBEAN OIL Filed Nov. 30, 1955INVENTOR United States Patent O REFINING F SOYBEAN (HL Herbert 3.Passino, Englewood, N. J., assigner to The M. W. Kellogg Company, JerseyCity, Tel. l.. a corporation of Delaware Application November 3l), 1955,Serial No. 549,928

4 Claims. (Cl. 26d- 4285) This invention relates to an improved processfor relining vegetable oils and more particularly to a process forproducing colorless neutral oil without caustic treatment of the oil.The process involves removing color bodies, fatty acids and otherimpurities from the oil in two steps: rst, eliminating color bodies andpolyfunctional fatty acids or fatty acids of high molecular weight bydissolving the oil in a low boiling solvent under paracriticalconditions, and second, eliminating the remaining fatty acids and moreeasily vaporized impurities by treatment with steam, ln a preferred formof the process, the condensate from the steam treatment is neutralizedand washed to remove soaps and the remaining condensate is returned tothe vegetable oil to restore certain minor components which help toprevent rancidity.

This application is a continuation-in-part of copending applicationSerial No. 463,559, tiled October 20, 1954, now abandoned, which is inturn a continuation-impart plication Serial No. 181,235, filed August24, 1950, and now abandoned, which in turn is a continuation-in-part ofapplication Serial No. 699,320, filed September 25, i946, and nowabandoned.

Vegetable oils such as soybean oil, cotton seed oil, linseed oil andpalm oil are obtained by pressing or solvent extraction of seeds, beansor other vegetable source in which they originate. Resulting oil istreated in various ways depending upon the nature of the oil, but inalmost every case, it is necessary to neutralize the oil by removal offatty acids and to decolorize it by removal of color bodies. At present,neutralizing is accomplished by treating the oil with caustic andwashing out the soaps. This step is usually accompanied by a loss of 3to 4% percent of the crude oil because some of the glycerides in the oilare converted into soaps along with the fatty acids. Decolorizing isordinarily accomplished by bleaching with clay, activated carbon, or ahydrated magnesium oxide. The nal bleached oil is treated with steamunder vacuum in order to deodorize the oil. In the case of certain oils,such as soybean oil, the above processing must be preceded by ahydrolysis step to remove phosphatides. The total loss encountered inrefining is commonly between 4 and 6 percent and sometimes even higher.

The present invention substantially reduces the cost of refiningvegetable oils and, in addition, reduces the losses to less than halfthat encountered in present commercial refining. Principally, thesavings are achieved by eliminating the neutralizing step and replacingit with two complementary steps for eliminating fatty acids. The fattyacids contained by the typical crude vegetable oil are mostly verysoluble in propane as long as they exist in their simple formuncomplicated by the substitution of hydroxyl or other groups forhydrogen in the acid structure. lf, however, some deterioration of theacid takes place, and there is a substitution of a hydroxyl group,ketone, or an alcohol, or some other group containing nitrogen,phosphorous, or the like, the solubility of the 2,802,849 Patented Aug.13, 1957 acid is radically changed, becoming very slight. atty acids arethus either among the most soluble or the least soluble components inthe crude vegetable oil; fatty acids of intermediate solubility are toominor to be of any concern. The phenomenon, the fact that almost all ofthe fatty acids in a crude vegetable oil are either of the very solubleunsubstituted type or the almost insoluble poly/functional type, makesthe present invention possible. Although it has never been possible toneutralize crude vegetable oils by steam treatment because there alwaysremained polyfunctional acids which would not vaporize out of the oil,the present process makes possible adequate commercial neutralization,that is neutralization to reduce the fatty acid content of the oil to0.05 percent or less, without chemical neutralization, by eliminatingthe polyfunctional acids in a solvent fractionation, followed by steamtreating to vaporizc the unsubstitued fatty acids from the oil.

Although the process is applicable to almost any vegetable oil whichrequires neutralizing and decolorizing, its application may beconveniently illustrated by a description of the treatment of soybeanoil. The crude soybean oil is rst contacted with a solvent having arelatively low critical temperature, preferably under 450 F., andsubstantially all of the oil is dissolved in said solvent, leaving onlyabout one or two percent of the crude oil in a dense phase. Preferably,the oil is continuously charged to a counter-current fractionation orextraction zone. The fractionation is carried out in a temperature rangebetween the temperature of maximum miscibility of solvent and oil andthe critical temperature of the solvent-oil mixture. The temperatureemployed usually falls in a range of about F. below the criticaltemperature of the solvent-oil mixture. Within this range, themiscibility of the oil and the solvent may be controlled withconsiderable precision because the density of the solvent, and hence itssolvent power, decreases with increasing ternperature (or decreasingpressure); as explained hereinafter, this phenomenon makes it possibleto reject from the oil a predetermined least soluble fraction thereof.in this first step of the process, the least soluble color bodies, fattyacids, and the like are eliminated, in a bottom fraction amounting tobetween about l.5 and 5 percent of the oil, usually in a fraction ofless than 2 percent. These least soluble materials arc also thematerials which have relatively high molecular weight and high boilingpoint. Although most of the color bodies are thus eliminated, a fewcoloring materials of low molecular weight and high solubility remain.Furthermore, the lighter weight fatty acids remain. A second step istherefore necessary to remove the impurities which could not be rejectedin the solvent treatment. The low molecular weight, low boiling pointimpurities are eliminated by subjecting the extract oil (preferablyafter the removal of all or most of the solvents) to treatment undervacuum with steam. It will be seen from this brief description that theinvention broadly comprehends two steps: rst, the rejection ofrelatively heavy impurities by solvent treatment and second, theelimination of the relatively low molecular irnpurities by evaporatingthem with steam. In another preferred `form of the invention these twosteps are augmented by a second solvent treatment step. In one mode ofpracticing the invention, the extract phase from the solvent treatmentis subjected to a second solvent treatment at higher temperature orlower pressure or both so as to precipitate substantially all of theoil, leaving only about 0.5 to l5 percent, preferably' about l percent,in the extract phase; the small overhead is only suicieutly large tocarry with it substantially all the remaining fatty acids and otherundesired impurities.

Although the condensate from the steam treatment is ordinarily comprisedof at least 50 percent fatty acids,

which are in no way desirable in the refined oil, it also containscertain complex substances which are present only as traces in the rawoil but serve an important function, that of enabling the raw oil toresist rancidity. It has been found that the deodorized oil is lessstable and will go rancid faster than raw oil, but that the stability ofthe oil can be substantially restored by restoration of the condensateresidue left after removal of fatty acids. It is a preferred species` ofthe present invention to neutralize the condensate, wash out soaps whichare formed and restore the neutral condensate residue to the refinedoil.

The oil from the fractionation zone may, if desired, be partially orentirely treated in a second countercurrent fractionation zone with thesaine or a similar solvent for the purpose of removing a small fractioncontaining the sterols, tocopherols, as Well as some of the free fattyacids and a small portion of the glyccrides.

It will be seen from the above brief description of the present processthat only two steps are required to obtain an oil having; all thedesirable characteristics for use in either the paint industry or in thefood industry. In the past it has always been necessary to treat thecrude soybean oil with caustic in order to remove the free fatty acids.The treatment with caustic not only involves considerable losses. basedon the crude oil, but also involves considerable difficulty in theremoval of the soaps from the oil as well as the removal of occluded oilfrom the soaps. Furthermore, the method involving the treatment withcaustic invariably results in the saponifcation of some of theglycerides, thereby increasing the losses. In addition, the causticcauses various chemical reactions to occur in the oil which produceundesired results. The present process avoids all of the disadvantagesof treating the oil with caustic since the oil is at no time treatedwith chemicals of any kind. All of the undesirable materials areeliminated from 'the crude soybean oil by countercurrent contact with asolvent in a fractionation Zone. According to the present process, therefining losses are reduced to less than one half of those previouslyencountered so that thc total yield of deodorized, decolorized, refinedsoybean oil amounts to about 97 percent or higher.

The solvents having the desired characteristics are normally gaseous andmust be used under such conditions of liquefying pressure that therenuircd degree of solvency for the soybean oil is obtained. Thesolvent, in the liquid state, and the soybean oil are continuouslycontacted preferably in a countercurrent fractionation zone under suchconditions of temperature and pressure that two homogeneous mixtures orphases having different densities are obtained. The upper or lighterphase consists principally of the solvent and the desired portion of theoil while the lower or heavier phase consists of the undesiredphosphatides, color bodies, polyfunctional fatty acids and mucilaginousmaterial and a very small portion of the solvent. The solvents, whichmay be used for the present process, must exhibit the characteristic ofhaving decreased solvent power for various components of the oil as thetemperature is increased. ln addition, the range of temperaturesemployed must be substantially below those temperatures at which anythermal decomposition or chemical reaction occurs in the soybean oil.Preferably the solvent should have a critical temperature well below thedecomposition temperature of the soybean oil, i. e., not substantiallyhigher than 450" F. and preferably below 325 F. The miscibility of thesoybean oil and such solvents decreases with increases in temperature inthe paracritical range between that temperature at which there issubstantially complete misciblity of the solvent and soybean oil, i. e.,about ltltl" below the critical ternperature and a higher temperaturenot substantially greater than the critical temperature of the solvent.At the higher temperature, the soybean oil and solvent are substantiallyimmiscible.

The low molecular weight hydrocarbons are particu- Cil larly suitablefor use in the present process since they exhibit the above necessarycharacteristics. The low molecular weight paraffin hydrocarbons areespecially useful since they are inert to substantially all componentsof the soybean oil. The low boiling, normally gaseous and normallyliquid paraffin hydrocarbons such as methane, ethane, propane, thebutanes and the pentanes are, therefore, preferred as solvents` but ithas also been found that the corresponding olen hydrocarbons may be usedwith satisfactory results and these latter compounds are, therefore, notexcluded. Since propane exhibits all of the desired characteristics to ahigher degree than some of the other solvents mentioned, it is thepreferred solvent for the present process. Furthermore, mixtures of anytwo or more of the above-mentioned hydrocarbon solvents may be used aswell as the relatively pure compounds. In addition to those solventspreviously mentioned, other solvents having relatively low criticaltemperature may also be employed, such as ammonia, ethylene oxide,dimethyl ether and methylamine and halogenated hydrocarbons such asdichlorodiuoromethane.

According to the present process the solvent and the desired portion ofthe oil is tallen overhead from the countercurrent fractionation zonewhile the less desirable portion, i. e., the phosphatides, mucilaginousmaterials, as well as some of the color bodies and fatty acids, isremoved fro-m the bottom of said zone. lf desired, the overhead fractionmay be treated similarly in order to remove an overhead fractioncontaining some of the unsaponiiiable materials including the sterolsand tocopherols, as well as sorne of the free fatty acids and a minorportion of the glyccrides. The material withdrawn from the bottom ofsaid second fractionation zone or the overhead fraction from the firstfractionation zone may be treated with steam under vacuum to remove odorforming materials, whatever free fatty acids remain and at the same timeeffect a striliing decolorization of the soybean oil, which will bediscussed further hereinafter. If desired, intermediate fractions forspecial purposes may be removed from either of the countercurrentextraction zones.

The accompanying drawing illustrates a ow sheet of a system for treatingcrude soybean oil according to the present invention. The drawingillustrates all of the essential features of the system schematically,but does not include various mechanical details which are well known tothose skilled in the art.

Crude soybean oil which has been expressed or extracted from thesoybeans is introduced through line 11 to fractionation tower 12. Inorder that the temperature of the soybean oil may be raised to thedesired level, a heater 13 is provided in line 11. The oil may beintroduced through any one or more of valved lines 14, 1S. and 16disposed intermediate thc ends of the fractionation tower 12. Propane isintroduced near the bottom of tower 12 through line 17 which may beprovided with a heater 18 to raise the temperature to the desired level.When the crude soybean oil is introduced into the fractionating tower atan intermediate point thereof, the lower portion of said tower willoperate as an absorption or stripping zone while the upper portion,above the point of introduction of the oil, will serve as arectification zone as will be described more fully hereinafter. As thepro pane rises through the tower 12 from its point of introductionthereinto, and the oil descends therethrough, a countercurrentextraction of the soybean oil is effected and those components of theoil, such as the phosphatidcs. the mucilaginous materials as well assome of the color bodies and fatty acids, which are insoluble orimmiscible with the propane, at the conditions employed, will flow tothebottom of tower 12 where they may be withdrawn from the system throughvalved-line 19.

The overhead from tower 12 may be passed through line 20 to separator 21where the propane solvent may be separated from the dissolved fattymaterials by evaporation or the like. The separated propane may bereturned to the storage tank 22 through lines 23, 24, and 2S. Theoverhead from tower 12 consists essentially of propane solvent havingdissolved therein the oily material and glycerides which are containedin the soybean oil. Since a substantial amount of the undesirablematerials have been removed from the overhead fraction, the oilymaterial which is removed from the bottomof separator 21 through line 26has a lighter color than the original oil. In order to remove furthercolor bodies or pigments from the oil, and in order to improve its odorcharacteristics, the oil may be passed through lines 27 and 28 to asecond fractionation tower 29. Additional propane may be introduced nearthe bottom of tower 29 through line 30 in a manner similar to thatdescribed in connection with tower 12. The fractionated oil fromseparator 21 may be introduced into the second tower 29 through one ormore of valved-lines 31, 32, and 33 at points intermediate the ends ofsaid tower. However, the conditions of temperature and pressure infractionation tower 29 are maintained so that a small overhead fractionis obtained which contains most of the unsaponitiable materials such asthe sterols and tocopherols as well as free fatty acids and a minorproportion of the giycerides. This overhead is withdrawn from tower 29through line 34 and is passed to a separator 35 for removal of propanecontained therein. The removed propane may be returned to storage tank22 through lines 36, 24, and 25.

When it is desired to pass vall of the overhead from fractionation tower12 to the fractionation tower 29, it will be advantageous to circumventseparator 21 by passing all of the overhead from tower 12 through lines20 and 29a directly into tower 29 through one or more of lines 3l, 32,and 33. Or if desired, a portion of the overhead from fractionationtower I2 may be introduced into the separator 21 for removal of solventtherefrom and the remaining portion of the overhead may be bypassedthrough line 29a directly to the fractionation tower 29.

It will be clear that when the overhead from tower 12 is passed directlyto tower 29 without the intermediate removal of propane in separator 21,the quantity of propane to be introduced into the bottom offractionation tower 29 through line 30 need only be sufficient to makeup to the desired propane-soybean oil ratio. On the other hand, it ispossible that less propane will be necessary for effecting the desiredseparation in fractionation tower 29 than is present in the overheadstream from fractionation tower 12 and, in this case, the desired ratioof propane to soybean oit may be obtained by passing a portion or 4allof the Overhead from tower 12 through the b separator 21 to remove onlythe undesired portion of the propane therefrom and subsequently passingthe remaining material from the bottom of separator 21 through lines 26,27, and 2S to fractionation tower 29.

If desired, a portion of the material withdrawn through line 26 from thebottom of separator 21 may be returned to tower 12 for reiluxing bypassing it through line 37. Also, if desired, a portion of the materialwithdrawn from the bottom of tower 29 may be passed through line 38 intoline 37 for reuxing as will be described more fully hereinafter. The oilwhich is withdrawn from the bottom of tower 29 is normally passedthrough line 39 to separator 4t) for removal of any propane which hasbeen dissolved in the oil. If desired, the propane may be removed inseparator 4t) by introducing steam through line 41 to assistvaporization of the propane. In this instance, the vapors withdrawn fromthe top of separator 40 through line 42 are passed to a condenser 43where the steam is condensed and water withdrawn through line 44. Thepropane is passed overhead through line 45 to line 24 and thence tostorage tank 22 through line 25. The depropanized oil is passed from thebottom of separatorfr40 through line 46 to a point near the top ofstripping tower 47. Steam is introduced into the bottom of saidstripping tower 47 through line 48 and passes upwardly through thecolumn of oil introduced at the top thereof. The overhead from thestripping column 47 consists of steam accompanied by any free fattyacids which might still remain in the oil as well as odoriferousmaterials. This mixture is passed through line 49 to a condenser 50where the Water, fatty acids, and odoriferous materiais are condensedand withdrawn through line 51. Any propane which might have accompaniedthe overhead from the stripper tower 47 is returned to the systemthrough lines S2, 24, and 2S to the propane Storage tank 22. The retinedsoybean oil is withdrawn from stripper 47 through line 53.

There is evidence to indicate that the tocopherols and possibly othermaterials function in the nature of inhibitors against color and tastereversion in the refined soybean oil, and it is, therefore, at timesdesirable to leave some or all of the tocopherols as well as some of thesterols in the nished oil. To accomplish this the small overheadfraction, which contains the sterols, tocopherols, as well as some ofthe free fatty acids and glyccrides, is not removed from tower 29 butrather the overhead from fractionation tower 12 is rst passed toseparator 21 through line 20 for recovery of the propane, and thebottoms'from separator 21 are then passed through lines 27 and 54 forintroduction directly into the stripper column 47. However, since thetocopherols have a rather high pharmaceutical value, it is sometimesadvantageous to remove at least a part of the tocopherols and sterolsfor separatetreatment. If it is desired to remove some of the sterolsand tocopherols, but at the same time, retain a small percentage thereofin the finished oil, this may be accomplished, for example, by passingthe soybean oil through fractionation tower 12, separator 21 thenthrough fractionation tower 29 and separator 35. A part of the bottomsfrom separator 35 may be returned to tower 29 through line 5S forreuxing. The remainder of the bottoms from separator 35 may be withdrawnfrom the system through line 56 for further treatment as statedhereinbefore, or a part or all of the bottoms may be added to thefinished oil by passing the same through lines 57 and 58 to line 53. Onthe other hand, if it is desired to remove any free fatty acids whichmight be contained in this fraction of the oil, it may be passed throughlines 57 and 59 to a neutralizer 6i! for treatment with caustic so thatthe fatty acids can be removed as soaps through line 61. The remainingmaterial consists largely of the sterols and tocopherols and iswithdrawn from the neutralizer 60 through line 62 and is added to thefinished oil in line 53 for inhibiting odor and taste reversion.

lt will be noted that the propane solvent is continuously recycledthrough the system. It passes first from storage tank 22 through lines17 or 30 to the fractionation towers 12 or 29 respectively. The overheadfrom each of the separators 21 and 3S and condeusers 43 and 5d isreturned through lines 23, 36, 45, and 52 to line 24 and then to line 25and the storage tank 22.

it will be understood that the various methods for recovering thepropane from the various fractions may be carried out by any of the wellknown methods. This may be accomplished by heating the overhead materialto cause evaporation of the propane which is subsequently condensed, orthe fractions may be heated to a point near the critical temperature ofthe propane to cause a phase separation between substantially all of thefatty material and the propane. In addition to these methods, thepropane may be removed from the overhead products by steam strippingwith subsequent condensation for the removal of water from thepropane-steam mixture. Furthermore, if desired, a combination of two ormore of the foregoing methods for recovery of the propane may be used.

When crude soybean oil is introduced through line 11 to thefractionating tower 12, a maximum temperature is maintained at the topof the tower and a minimum temperature at the bottom of said tower. Thebottom P temperature may be conveniently controlled by the temperatureof the propane being introduced through line 1'7. The soybean oil, whichis introduced through line 11, may be heated to the same temperature asthat of the propane, so that the temperature between the soybean oil andpropane charge points is substantially uniform, or if desired, thesoybean oil may have a higher temperature than the propane so that therewill be temperature gradient between the charge points.

The lower portion of the fractionating tower 12, below the charge pointof the soybean oil, functions primarily as an absorption zone in whichthe components of the soybean oil which are not absorbed or dissolved bythe upwardly fiowing propane stream, ow downwardly through the tower byreason of their greater gravity. As the fatty material flows downwardly,it contacts propane which is less saturated with respect to the fattymaterial, so that more of this material is eventually absorbed ordissolved in the propane phase. The unabsorbed or undissolved material,such as the phosphatides, mucilaginous materials, color bodies and fattyacids, is collected at the bottom of the fractionating tower 12 and iswithdrawn through line 19. The interface between the propane phasecontaining dissolved fatty material, and the undissolved phase may bemaintained above o1' below the propane charge point. However, in orderto obtain a better stripping effect on the undissolved phase, thisinterface should be located above the propane charge point.

As the propane phase containing dissolved fatty ma teriar rises upwardlythrough the tower above the oil charge point, it may be progressivelyheated to slightly higher temperatures by means of heating coils (notshown) of any conventional type. As this phase moves upwardly throughthe upper portion of the tower, those portions of the fatty materialwhich become less soluble and which are undesired in the final product,are precipitated as a separate and heavier phase, containingsubstantially less propane than the propane-fatty material phase. Thisprecipitated material iiows downwardly from the point of precipitationin countercurrent contact with the upwardly flowing propane phase andpasses from a higher temperature to a zone of lower temperature at whichthe capacity of the propane phase to absorb the oil is greater than atthe temperature at which the precipitated material was precipitated.Therefore, the propane phase ends to reabsor'o oil which has beenprecipirated from the propane phase at a higher temperature and at ahigher point in the fractionation tower 12. It will be seen, therefore,that a highly ciiicicnt rectifica tion of the fatty material is obtainedand that the precipi u tated material constitutes a highly efficientreliuxing in the upper portion of the tower.

if desired, refluxing by precipitation as described above, may be usedinstead of relluxing by introducing a portion of the product throughline 37 to a point near the top of tower 12. Or if desired, both typesof retiuxing may be used. The degree of efticiency in the removal ofundesirable constituents from the crude soybean oil is largely dependentupon the etlciency of reiluxing and it is, therefore, usually desirableto utilize the most efficient reflnxing in order to obtain a highlyrefined deodorized and decolorized soybean oil without excessive losses.

In order to improve the reiluxing in tower 12, it may be sometimes founddesirable to pass a portion of the bottoms from tower 29 through line 38and line 37 f to the top of tower 12. This modification will enrich thematerial at the top of tower 12 with the desired components of thesoybean oil and will, therefore, tend to decrease the solvent power ofthc propane for various undesired components which might, except for thereuxing, tend to be carried overhead with the desired products throughline 20.

The maximum temperature generally employed at the top of tower 12 may behigher than the critical temperature of the propane or other solvent,but it is ordinarily preferred to operate at temperatures below thecritical temperature and falling within the range of temperature betweenthe critical temperature and F. below said critical temperature. Withinthis range of temperatures, the lower temperatures are employed at thetop of the tower when it is desired to obtain an overhead fractioncontaining a relatively greater proportion of the crude soybean oil,whereas higher temperatures within this range are employed whenrelatively smaller proportions of highly refined soybean oil aredesired. In the latter cam, the overhead product will have a very highdegree of purity since all of the impurities will be removed from thebottom of the tower. It will, therefore, be seen that the particulartemperatures involved, especially at the top of the fraetionating tower12, have considerable effect on the amount of refined soybean oil to befinally recovered and in general, greater refinement is obtained whenthe amount of the overhead product is reduced.

Another factor which affects the degree of refinement to a great extentis the relative quantities of crude soybean oil and propane which areintroduced into the fractionating tower 12. Considerable renement isobtained when the propane to soybean oil ratio is about 5:1 by volume.However, far better refinement is obtained with greater yields ofrefined product when this ratio is increased to 10:1, 30:1, or 50:1, oreven higher. For example, when a propane to soybean oil ratio ofapproximately 30:1 is used, it is generally necessary to remove onlyabout 1.5 percent of the crude soybean oil as bottoms in order to removesubstantially all of the phosphatides, muclaginous materials as well assome of the color bodies and polyfunctional fatty acids. These lossesare far less than those encountered by the use of previously knownprocesses. When relatively higher ratios of propane to soybean oil areused, the proportion of oil absorbed by the solvent is greater and themaximum temperature at the top of the tower 1.2 must be established withrespect to the solvent to soybean oil ratio.

The temperature at the bottom of the tower must, of course, be abovethat temperature at which complete miscibility of the solvent and thesoybean oil in the lower portion of the tower occurs. The preferredbottom temperatures are generally maintained at from about 5 to about F.or more below the critical temperature of the solvent. When propane isemployed as a solvent in the refinement of soybean oil, the temperatureat the top of the tower may be between and 200 F. and the bottomtemperature may be between 140 and 190 F.

The pressure employed in the fractionating tower 12 is maintainedsufficiently above the vapor pressure of the solvent to permitsubstantial variation in the tower pressure without reducing it belowthe vapor pressure of the solvent. A maximum operating pressure ofapproximately 50 pounds per square inch higher than the vapor pressureof the solvent is generally sufficiently high since adjustments of 10 to15 pounds per square inch in the operating pressure are usuallysufficient to counteract whatever temperature variations may occur inthe operation of the tower. For example, the pressure in the tower 12may be between about 400 and about 490 p. s. i. g., but is notrestricted to this range.

When `a portion or all of the partially refined soybean oil isintroduced into fractionating tower 29, the temperatures requiredtherein, in order to remove a small overhead fraction containing thesterols, tocopherols, free fatty acids, etc., are higher than thoseemployed in the first fractionating tower 12 while still falling withinthe range of temperatures previously defined. For example, thetemperature at the top of fractionating tower 29 may `be between 165 and210 F. while the temperature at the bottom of this tower may be betweenand 195 F. Since the temperatures employed in fractionating tower 29 areslightly higher than in tower 12, it is also necessary to operate thistower at a slightly higher pressure. For example, the pressure in thetower 29 may be between about 510'and 590 p. s. i. g., but is notrestricted to this range.

As previously stated, when. an eiticient operation of towcrlZ isemployed, the material withdrawn through line 19 constitutes only about1.5Y percent of the crude soybean oil while the remaining 98.5 percenttogether with the propane Vis'passed to fractionation tower 29. Duringefficient operation of this latter tower, all of the sterols,tocopherols, as well as some free fatty acids, may be completelyVretrieved from the soybean oil by with- V'drawing from 0.5 percent to1.0 percent overhead based on the crude soybean oil. The materialwithdrawn from tower'29 through line 39, therefore, constitutes from97.5 percent VYto 98 percent of the original oil and since a practicalyynegligible quantity of material is removed in steam Vstripper 47, thefinal product will constitute from about 97 percent or higher of thecrude oil. Though a Vnegligible amount of material is removed in steamstripper 47, it has been found that this separation when used 'Ysubsequently Vto the propane fractionation steps previous- VAso'ylnfarioil.

Vfact that a total of less than 3 percent of the original crude oil hasbeen removed. Not only is this decolorization step remarkable but it hasalso been found that the stability of the oil treated according to thepresent process, both as to odor and color, is greatly improved. Inother words, it has been found that a highly decolorized soybean oilobtained by a treatment, according to the present invention, will retainits exceptional color property for a much longer period of time than waspreviously the case.

In order to eiectively strip the soybean oil in stripper 47, it isgenerally best to maintain the stripper at a pressure about between 1mm. and 20 mm. but preferably within the range of from about 8 mm. to l2mm. The temperature of this operation and of the steam being introducedinto the stripper is usually between about 350 F. and 500 F., but atemperature of about 425 F. has been found to be most suitable.

Example I Tests of a typical neutralization of soybean oil by thepresent method reveal the following fatty acid contents: Percent fattyacids VThe above example reveals that only l percent of the originalfatty acids were removed by the propane fractionation. This is not to beconsidered insignificant, howover. This l0 percent comprises 0.05percent of the original oil, which would be more than could be toleratedin satisfactorily neutralized oil. Moreover, the example above is'talrenfrom the treatment of first grade fresh `soybean oil. vIn the case ofinferior oils, to 30 percent of the fatty acids were removed in thebottoms fraction of the propane fractionation.

The stability as to odor and flavor is also improved by the foregoingtreatment. However, soybean and other vegetable oils tend to acquireobjectionable odors and tastes under certain conditions of usage orstorage.

Example II Soybean oil was decolorized in a 4-inch battled tower as astripping tower and a 2-inch tower packed with 1%- iuch Lessing rings asthe rectifying tower. A propane stream was dvided'with equal portions,8.40 percent by weight, being introduced at the l6-foot point of thestripping tower and at the l-foot point of the rectifying tower. With atower top temperature of 165 F. and a bottom temperature of 158 F., anoverhead product amounting to 97.6 percent was made using a reflux ratioof 0.65, based on the overhead.

The decolorized overhead product was then refractionated using'a pair ofIS-foot towers two inches in diameter, with a propane to oil ratio of29.8 by volume. The oil feed rate was 3,000 ce. per hour and the towertemperatures were 193 F. top and 176 F. bottom. Using a redux ratio of56.4 based on overhead, the yield of the overhead product amounted to1.6 weight percent.

The data are as follows:

TABLE I Propane fractionation in countercurrent towers-Tabulation ofdata-Soybean oil Percentage of Orlgtnal O11 100 l 96. 2 Type ofOperation Temperature Gradient+ Reflux No. of Towers,-- 2 Yields andBalances (Output Basis):

011- Weight Percent- 97. 6 1. 6 2. 4 98. 4 Weight Balancc, 102. 1 102. o

Free Fatty Acid Recovery, Percent- Overhead 91. 7 81. 4 Bottoms 1. 9 15.9

Total 96. 6 9?. 3

Unsaponiable Oil Recovery, Percent- Overhead 99. 0 48. 8 Bottoms 3. 945. 6

Total 102. 9 4

Operating Conditions: Tem erature, F.-

op 165 193 Feed 158 182 Bottom 158 170 Temperature Gradient, FJFtRectifylng Section O. 28 0. 55 Stripping Section 0. 0D 0. 50 Throughput,Lo/HTJSQ. Ft.-

Fractionating Tower (Z-in. Tower):

Oil 261. 5 261. 5 Propane 4, 290 4, 290 Propane Velocity, ft.

Fractionatlng Tower (2-ln. Tower) 136. 5 138. 5 Propane-Oil Ratio (ByVolume, 60)- Fracttonattng Tower 2 30. l) 29. B Propane-Oil Ratio, ByWeight- Fractonating Tower 2 16. 4 16. 4 Contact Time. Mtn.-

Fractionating Tower 36. 8 15. 3 Redux Ratio 0. 65 56. 4 Height ofRectifying Section, t 25 20 Height of Stripping Section, Fn 7 12 OilProperties:

Feed- Color, Lovbond:

Red. Yellow Color Gardner Free fatty acids, Percent (as 01ste)Unsaponiabie Oil, 't. Percent.. Saponlcation No Iodine No. (Wijs)Moisture and Volatility, Wt. Percent Acctonc Insoiuble, Wt. PercentGardner Break Specific Gravity (60/60) Fractlonator Overhead- Color,Lovibond:

Red.

Yellow. Coior, Gardner 9 8- Free Fatty Acids. Percent (As Olcic) 0.6534. 6 Unsaponiablc Oil, Wt. Percent o. 71 29. t) Saponitcation No 19213S Iodine N o. (Wijs) 127 Moisture and Volatility, Wt. Percent SpecificGravity (BIP/60) 0. 919 0. 917

Bottoms- Color, Gardner 15+ 10- Free Fatty Acids, Percent (As 01eic) O.54 0. 11 Unsaponabie Oil, Wt. Percent 1.15 o. 44 Iodine No. (Wijs) 141134 Saponicaton No 196 192 Abetone insoluble, Wt. Percent 1. 9 Moistureand Voiatility, Wt. Percent Specific Gravity (6W/60") 0. 934 0. 919

1 l TABLE I-Continued Observed Yields:

Oil, Weight Percent- Fraetionator Overhead Sample 0117 1. 6 r Bottoms2.4 101.0

Free Fatty Acid Recovery, Percent- Overhead 96. 8 81.4 Bottoms 1. 9 16.3

Total 98.7 ".7 10

Unsaponiflable Oil Recovery, Pereent- Overhead 101.1 48. S Bottoms 3. 946. 8

Total 105.0 95. 6

Detailed Operating Conditions:

Flow, Gin/Hr.-

Fecd 2, 772 2, 773 Propane to Froetionator i 45, 500 45, 500Fractionator Overhead Sample.-- 2, 763 43 Bottoms G0 2, 802 Reflux (Oil)1,790 2, 430 Intermediate Overhead-. 3, 510 1,520 Intermediate Bottoms799 1,470 Propane-Oil Ratio (Stream Sample Overhead Receiver 0. 0.30Intermediate Bottoms. 2. 2. D Pressure, lll/sq. in. Ga.-

Fractonating Tower 490 570 Overhead Receiver 350 460 25 Temperature, F.-

E-2 Tower:

Transfer Line Position of Entering Streams Top of Tower, Ft.)-

Strilping Tower (18 Twr., 4 Dia.) (E-l):

ee 9 4 Propane 2 16 16 Ratlinato Rectifying Tower 1 1 Reotifying Towertl'Twr., 2" Dia.) (IE-2):

Reflux 4 4 45 Extract Stripping Towcr 16 16 Propane 2 16 l Overheadproduct-contains somo unoiicial material. 2 Propane stream divided-Equalamount to each tower.

Freshly refined soybean oil made from a crude oil derived from highgrade beans has a characteristic odor but is bland and sweet. It can beconsidered to be highclass salad oil since the characteristic odor isnot objectionablc. However, when heated to 425 F. in a socalled cookingtest, a sharp, grassy odor develops. The chief drawback of refinedsoybean oil is that in the course of from a few days to months,depending upon conditions, the oil undergoes a peculiar change which isknown as reversion This deterioration is accompanied by the developmentof an undesirable odor and flavor which has been variously described ascucumbery, "grassy, painty, or fishy. There is undoubtedly a progressivechange in odor and flavor, and the odor is not the same at the beginningof the reversion period as toward the end. The process is not true odorreversion because the odor does not revert to that of either the crudeoil or the undeodorized oil.

lt should. be observed that reversion and oxidative rancidity arcdifferent, although possibly related, phenomena. Corn oil, one of thebest food oils, causes little trouble because of reversion but becomesrancid more rapidly than soybean oil as measured by peroxide formation.Attempts to correlate soybean oil reversion with peroxide values havenot led to fruitful results.

A tremendous amount of research effort has been expended in attemptingto prevent soybean oil reversion and to determine the underlying cause.The theory that has attracted the largest following in recent years isthat soybean oil reversion is due to the presence of a small percentageof linolenic acid, an unsaturated fatty acid containing three doublebonds, in the glyceride molecules. Corn and cottonseed oil, which arenot subject to much reversion, do not contain a detectable amount oflinolenic acid. On the other hand, linseed oil which contains a highpercentage of linolenic acid is characterized by a typical strong paintyodor. According to this theory, the linolenic acid decomposes in storageto odoriferous substances because of oxidation with air, condensation,ring closure, or some unknown kind of reaction.

On this assumption work on the reversion problem has been directedtoward the elimination of linolenic acid. Since it is impractical inthis case to remove the linolenic acid by hydrolysis of the glyceridesand separation of the fatty acids, the main line of attack has beenpartially and selectively to hydrogenate the oil with the objective ofconverting the linolenic acid to a more saturated acid such as linoleic.Unfortunately, the partial hydrogenation has not been amenable toselectively control with the result that stearines and solid isomericunsaturated acids are formed to an undesirable extent. Futhermore,reversion is not entirely prevented and the oil acquires in addition agassy odor.

The invention herein disclosed makes it possible to remove the freefatty acids, including substantially all of the free linolenic acid,without neutralization treatment of the oil. Decolorizing isaccomplished without the use of any bleaching agent or adsorbent meansin the body of the oil. All or a part of the condensate recovered fromcondenser 50 through line 51 may bc subjected to neutralizing treatment(preferably with aqueous alkali solution) and to decolorizing by meansof carbon or clay filter beds or to bleaching by heat, steam, orchemical treatment. The neutralized or decolorizcd condensate may thenbe washed with water to remove soaps and residual alkali and returned tothe refined oil.

The refined soybean oil, according to the present invention, will meetthe severest standards required in both the paint and varnish industryas well as the food industry. This refined material may be obtained farmore efficiently and by a method which is far simpler than those methodspreviously used. In addition, the product so obtained has less odor andcolor reversion and far smaller losses are incurred during theprocessing of the oil.

The present invention has been described with particular reference to aspecific embodiment thereof, but it will be recognized that I do notintend to be limited by this description, but rather that the scope ofthe present invention should be defined solely by the appended claims.

I claim:

l. A method for refining vegetable oil which includes the steps of:contacting said oil with a solvent having a critical temperature of lessthan 450 F. under paracritical conditions to fractionate said oil intoan extract phase containing substantially all of said oil and araffinate phase containing color bodies and substantially all thepolyfunctional acid content of said oil; withdrawing said extract phaseand subjecting the extract oil contained therein to treatment with steamat a temperature between 300 F. and 500 F. to vaporize volatilematerials; condensing said vaporized materials and neutralizing themwith an alkali; and recombining at least part of said neutralizedcondensate with said extract oil.

2. An improved process for producing a refined neutral soybean oil byfractionation with a solvent having a critical temperature ot' less than450 F. under paracritical conditions, which process includes the stepsof: contacting said oil with said solvent in a first vertically extendedcountercurrent fractionation zone at temperatures adjusted within theparacritical range to form two counterflowing phases, an extract phasecontaining substantially all of the oil, and a rainate phase containingsubstantially all of the polyfunctionai fatty acid content of said oil;contacting at least part of said extract phase with said solvent in asecond fractionation zone to form a secondary extract phase containingsubstantially all the unsaponitable content and a secondary ratiinatephase containing most of the oil; withdrawing said secondary extract andrainate phases from the upper and lower ends respectively of said secondfractionation zone; subiecting the oil content of said secondary rainatephase to treatment with steam at a temperature between 350 F. and 500 F.to remove vaporizable impurities and substantially all remainingunsubstituted fatty acids; and combining at least part of thennsaponiiiable concentrate in said secondary extract with said secondaryraftinate after said steam treatment.

3. A method for refining vegetable oil which includes the steps of:contacting said oil with a solvent having a critical temperature of lessthan 450 F. under paracritical conditions to fractionate said oil intoan extract phase containing substantially all of said oil and a raf- 14tinate phase containing color bodies and substantially all thepolyfunctionai acid content of said oil; withdrawing said extract phaseand subjecting the extract oil contained therein to treatment with steamat a temperature between 300 F. and 500 F. to vaporize volatilematerials; condensing, neutralizing with an alkali; and re* combining atleast part of said vaporized material with said extract oil.

4. A process as described in claim 3 in which prior to the recombinationof said condensate with said oil, said condensate is decolorized.

References Cited in the tile of this patent UNITED STATES PATENTS2,118,454 Schaafsma May 24, 1938 2,394,968 Van Orden Feb. 12, 19462,432,021 Lamer Dec. 2, 1947 2,454,638 Dickinson et al Nov. 23, 19482,508,387 Hixson et ai. May 23, 1950 2,521,234 Leaders et al. Sept. 5,1950

